In some applications of switching field effect transistors (FET) such as in high frequency switching converters or regulators, it is necessary to isolate the FET's control circuit, operating at a low voltage level, from the switching circuit of which the FET forms part, operating at a high voltage level, by means of a drive circuit.
In the case of space applications such a drive circuit should allow the FET's gate to be biased negatively with respect to its source in the "off" condition, since otherwise the ionizing radiation of the space environment could provoke the FET to switch on. Such negative gate bias also prevents switching of the FET in case of randomly occurring step voltages applied to the gate.
It is further required that for switching converters or regulators, the drive circuit's delay time in switching the FET "on" or "off" should be very short, i.e. in the order of 0.05 microsecond.
Finally, such a drive circuit should allow a zero to 100% duty cycle when driven by pulse width modulated signals, i.e. it should allow the FET to be switched fully "on" or "off" for an indefinite period of time.